4 January 2017 | Venus

Venus and Earth, two out of the four inner or ‘rocky’ planets of the Solar System, have a lot in common. It is amazing to compare some of the planetary features of Venus with those of Earth.

Their masses are basically the same, and their densities too. Their radii seem just copied from one planet to the other. Their distances from the Sun are not so different – Venus is about 108 million kilometres and Earth is 150 million kilometres.

Their rocks are both largely basaltic, result of intense volcanism and of a similar solidification process, initiated about at the same time, four and a half thousand million years ago, when the planets of the Solar System started to form from the solar ‘proto-planetary nebula’.

However, looking closer, Venus and Earth are worlds truly apart in many major aspects. Walking on Venus’s surface would be difficult, like walking under water at 900 metres depth (the atmospheric pressure at Venus is 90 times higher than on Earth at sea level) – and as uncomfortable as staying in an oven at 465 °C!

Venus’s surface is indeed the hottest in the Solar System. Despite only 10% of the solar flux reaching the surface, enough energy is trapped by gases and particles present in the lower atmosphere, to raise the temperature at the surface dramatically. A catastrophic ‘greenhouse effect’ is taking place.

Venus’s atmosphere is composed almost entirely of carbon dioxide, with very little water vapour. It has significant amounts of corrosive sulphur-bearing gases and rapidly moving clouds of sulphuric acid droplets. The dense clouds scatter back to space about 80% of the radiation received from the Sun. Scientists translate this concept into saying that Venus has a very high albedo.